A typical ultrasonographic device is conventionally constituted of an ultrasonic wave transmitter/receiver section for transmitting and receiving ultrasonic waves to and from a test subject, a tomographic scanning section for repeatedly obtaining tomographic image data in the test subject including motor tissue in a predetermined cycle by using a reflecting echo signal from the ultrasonic wave transmitter/receiver section, and an image display section for displaying time-sequence tomographic image data obtained by the tomographic scanning section. Further, the structure of living tissue in the test subject is displayed as, e.g., a B-mode image.
In relation to this device, in recent years, an external force is artificially applied from the body surface of the test subject through a pressurizer or an ultrasound probe to measure a distortion and/or elastic modulus of living tissue of an examined part, and the hardness of the tissue is displayed as an elastic image based on numeric data (elastic frame data) of a distortion or elastic modulus by using the ultrasonographic device. Such an ultrasonographic device is disclosed in JP-A-5-317313 or JP-A-2000-60853.
However, in the imaging of elastic frame data in the ultrasonographic device of the citations, a correlation operation is used between two RF signal frame data which are obtained in a series of pressuring or decompressing operations and are adjacent to each other in time sequence. Thus, when an amount of pressurization or decompression applied in a time interval between RF signal frame data constituting a group of two or more RF signal frame data does not sufficiently reach an amount of pressurization or decompression (generally about 1%) suitable for visualizing elastic image data, it is difficult to properly visualize an elastic image of elastic frame data.
During a series of pressuring or decompressing operations, when an object is diagonally and/or unevenly pressurized or decompressed, a time phase may occur in which a stress distribution in the object has a temporally irregular change. In such a time phase, a coordinate area where a stress distribution has a temporally irregular change appears in a series of elastic frame data (distortion data) in the time-base direction. Thus, an elastic image includes a temporally irregular area as noise, so that image diagnosis becomes difficult.